Comparative studies of magnetic properties in osmates with the double perovskite structure

Using the first-principles density functional approach, we comparatively studied the electronic and magnetic properties of two series of ordered double perovskite, Ba2BOsO6 (B = Sc, Y, and In) and A(2)ScOsO(6) (A = Ba, Sr, and Ca). The electronic structure calculations indicate that the Os ion bears the nominal t(2g)(3) state with oxidation state 5+ and is the only magnetically active one in all compounds. In nice agreement with the experimental observations, all of them stabilized in the type I antiferromagnetic alignment, which is mediated by the moderate nearest-neighbor antiferromagnetic interactions through the Os-O-B-O-Os 90 degrees route and accompanied by mild next-nearest-neighbor antiferromagnetic coupling via the Os-O-B-O-Os 180 degrees route, in spite of the geometric frustration. The mechanism of the antiferromagnetic interaction has been proposed based on the density of states analysis. In addition, the computed magnetic moment on Os ions, similar to 2 mu(B), is remarkably smaller than the ideal spin-only value. In conjunction with the modest spin-orbit coupling effect, strong covalency between the Os-5d and O-2p states reduces the magnetic moments. More importantly, our results demonstrated that the magnitude of the magnetic couplings as well as magnetic transition temperature T-N are directly proportional to the reciprocal of the absolute value of energy mismatch between the B-nd and occupied Os-t(2g) band; in addition, they are also a function of the Sc-O-Os bond angles, i.e., the buckling of the octahedral connectivity. Moreover, comparison of these two series helps to identify the energy mismatch as the efficient factor to adjust the magnetic interactions.